As far as I can tell, this issue is different than: https://bugs.python.org/issue34730

I noticed `async_gen.aclose()` raises a GeneratorExit exception if the async generator finalization awaits and silence a failing unfinished future (see example.py).

This seems to be related to a bug in `async_gen_athrow_throw`. In fact, `async_gen.aclose().throw(exc)` does not silence GeneratorExit exceptions. This behavior can be reproduced without asyncio (see test.py).

Attached is a possible patch, although I'm not too comfortable messing with the python C internals. I can make a PR if necessary.